The Reaction of Transient 1,1-Bis(trimethylsilyl)silenes with Tris(trimethylsilyl)silyllithium - Synthesis and Structure of Sterically Congested 1-Trimethylsilylalkylpolysilanes

摘要

Tris(trimethylsilyl)silyllithium (3) reacted with aldehydes and ketones (molar ratio 2:1) according to a modified Peterson mechanism under formation of transient silenes, which were immediately trapped by excess 3 to give the organolithium derivatives (Me_3SI)_3SiSi(SIMe_3)_2C(Li) centre dot R~1R~2 (7). Hydrolysis of 7 afforded the alkypolysilanes (ME_3Si)_3SiSi(SiMe_3)_2CHR~1R~2 (8). Depending on the substituents R~1 and R~2 , 7 proved to be rather unstable in THF solution and underwent a rapid rearrangement, involving a 1,3-Si, C-trimethylsilyl migration, resulting in the formation of the lithium silanides (Me_3Si)_2Si(Li)Si(SiMe_3)_2C(SiMe_3)R~1R~2 (9), which were hydrolized during the aqueous workup to give the H-silanes (Me_3Si)_2Si(H)Si(SiMe_3)_2C(SiMe_3)R~1R~2 (10). Reaction of 9 with chlorotrimethysilane produced the 1-trimethylsilylalkylpolysilanes (Me_3Si)_3SiSi(SiMe_3)_2C(SiMe_3)R~1R~2 (11). The structures of the products described were elucidated by comprehensive spectral analyses. The results of X-ray crystal structure analyses, performed for 81 (R~1 = H, R~2 2,4,6-(MeO)_3C_6H_2), 10 d (R~1 = H, R~2 = Mes) and 11 d (R~1 = H, R~2 = Mes) are discussedand confirm the expected extreme sterical congestion of the molecules.